In order to adjust a steering wheel position to a sitting position of a driver of a motor vehicle, steering columns are known in various configurations in the prior art. Besides a vertical adjustment by adjusting a tilt of the steering column, the steering wheel arranged at a rear end of the steering spindle in such steering columns can be positioned by a length adjustment in a direction of the steering column's longitudinal axis in an interior of the vehicle.
In order to adjust the steering wheel position to the sitting position of the driver of a motor vehicle, such steering columns are known in various configurations in the prior art. Besides a vertical adjustment by adjusting the tilt of the steering column, the steering wheel arranged at the rear end of the steering spindle in such steering columns can be positioned by a length adjustment in the direction of the steering column's longitudinal axis in the interior of the vehicle.
The length adjustability is realized in that the adjustment unit, which comprises the steering spindle mounted rotatably in a casing tube, is movable telescopically in the longitudinal direction relative to the supporting unit, which forms a support for the steering column that is firmly connected to the body of the vehicle, and it can be secured by means of a releasable clamping device in various lengthwise positions, i.e. it is releasably securable. The clamping device, also known as a securing device, acts on the adjustment unit held by the supporting unit, so that in the opened state of the clamping device—also known as the release position or loose position—a displacement of the adjustment unit relative to the supporting unit in the longitudinal direction is possible, for adjusting the steering wheel position, and in the closed state—called the securing position or locking position—the adjustment unit is clamped to the supporting unit and the steering wheel position in normal operation is secured under the anticipated mechanical stresses.
A steering column of this kind is described in DE 10 2008 034 807 B3. The clamping device described here comprises a clamping mechanism with an actuating element designed as a clamping axle. A rotary movement of the clamping axle exerted via an operating lever is converted by the clamping mechanism into a clamping stroke, which exerts a force in the transverse direction on the supporting unit, so that the adjustment device mounted therein is firmly braced, comparable to the function of a clamp. In this way, a force locking of the adjustment unit in the longitudinal direction is achieved.
As an effective measure for improving passenger safety during a vehicle collision, a so-called crash or frontal impact of a vehicle, during which the driver is thrown at high speed against the steering wheel, it is known how to design the steering column to be collapsible in the longitudinal direction, even in the securing position of the clamping device, when a large force is exerted on the steering wheel, greater than a limit value, which only occurs during a crash. In order to provide a controlled braking of a body impacting on the steering wheel, an energy absorption device is coupled between the supporting unit and the adjustment unit, which in normal operation are secured and clamped together by the clamping device as described, but in a crash are pushed together relative to each other. This converts the introduced kinetic energy into a plastic deformation of an energy absorption element, for example by breaking a tearing tab or bending an elongate long bending element, such as a bending wire or a bending strip, or by widening an oblong hole by means of a bolt or by stretching a sheet metal strip or by slicing off a shaving with a plane.
The activating of the energy absorption device (crash device) in known steering columns occurs by the clamping device when securing the adjustment unit. Specifically, for the crash activation, a locking part mounted on the supporting unit immovably in the longitudinal direction is likewise moved with the clamping stroke of the clamping device and is brought into form-fitting engagement with a form-fitting element, preferably a serration, with a corresponding form-fitting element, i.e. preferably a corresponding serration, of an engagement part. The engagement part is connected by an energy absorption device to the adjustment unit, which is not stressed during normal operation, i.e. it forms a rigid connection between supporting unit and adjustment unit. In the event of a crash, however, so great a force is applied to the adjustment unit that the adjustment unit and the supporting unit move in the longitudinal direction toward each other, whereupon the energy absorption element is deformed and thereby brakes the movement. The form-fitting connection between the locking part and the engagement part ensures that the fixed end of the energy absorption device can be securely braced by the engagement part against the supporting unit. In other words, in the event of a crash the form-fitting connection between the locking part and the engagement part remains intact, so that the energy absorption occurs in the energy absorption device, which is designed separately and functionally independent of the locking device. For the movement of the steering column, the clamping device is placed in the release position, whereupon on the one hand the clamping of the adjustment unit in the supporting unit is released and on the other hand the locking part is lifted by the reversed clamping stroke so much from the engagement part that the form-fitting elements get out of engagement and after an adjustment to a different position occurs they can be connected once again.
The crash activation upon actuation of the clamping device affords substantial additional safety to the vehicle passengers. However, it is a drawback of the prior art that the clamping stroke of the clamping device must be at least large enough so that a secure engaging and separating of the form-fitting elements of locking part and engagement part occurs during the locking and releasing, even though the clamping of the adjustment unit requires a smaller clamping stroke or even no clamping stroke, but only a clamping force. This restricts the design of the clamping device in terms of the clamping stroke and force transmission during the manual locking of the clamping device, when the functionality of the crash device needs to be assured.
From US 2010/0300236 A1 there is known a steering column with an energy absorption device. The energy absorption here, unlike the aforementioned DE 10 2008 034 807 B3, is supposed to occur in the clamping device itself in that the engagement part in the event of a crash slips through relative to the locking part, i.e. the form-fitting connection between the locking part and the engagement part is broken. The drawback here, however, is that the serration actually provided for the locking may produce an abrupt and hard to control energy absorption, which is therefore unsuitable in practice.
Thus a need exists to provide a steering column with a clamping device and a separate energy absorption device that offers improved possibilities of crash activation and that overcomes the dependency on a clamping stroke of a clamping device.